Q:
Misfire at hard thottle, rpms either dont go up when accelerating, or slowly drop as i accelerate

asked by
Edward K
on
October 25, 2016

My grand prix has began to hesitate and misfire under hard throttle, im unsure as to why which is why im asking here. This is whats been fixed and whats new on the car:

Mass Airflow Sensor

Manifold Absolute Pressure Sensor

Spark Plugs- NGK TR6

Spark Plug Wires- MSD Street Fire 8mm

Ignition Coils- all 3 of them

Vacuum lines running to map sensor and supercharger bypass solenoid

Supercharger Bypass Solenoid

Supercharger Bypass Valve

Accelerator Pedal Sensor

Fuel Pump- Airtex E3700M

After all this it still acted strange so I removed the fuel injectors and manually cleaned them aswell, and reinstalled with new o rings. Im at a loss as to what it is. It ran great for a long time, and I miss being able to run it like I used to. I am thinking maybe a camshaft position sensor but theres no codes to reflect that.
"on a side note, I checked tps with a scan tool, its ok, but the fuel trims are a bit erratic. Thank you for your help

My car has 187000 miles.
My car has an automatic transmission.

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Hi - check your vehicle’s fuel pressure when running, and under load. Your comment regarding "fuel trims ...erratic" gets my attention. If the pressure is not correct, check the fuel pump relay (possible burned contacts) and fuel pressure regulator. If the pressure is correct, I would suspect the injectors need professional cleaning and testing - given your mileage. I would recommend having an Engine is Misfiring Inspection completed by a mobile, professional mechanic, such as one from YourMechanic, to diagnose this problem, get an accurate assessment of damage and cost estimate for repairs.

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